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</div><h2>HL Paper 3</h2><div class="specification">
<p class="p1">The colour of olive oil is due to pigments such as chlorophyll, pheophytin and carotenoids.</p>
<p class="p1">The absorption spectrum of one form of pheophytin is shown below.</p>
<p class="p1" style="text-align: center;"><img src="images/Schermafbeelding_2016-08-08_om_08.31.40.png" alt="m15/4/CHEMI/HP3/eng/TZ2/28"></p>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">State the structural feature of a pheophytin molecule which allows it to absorb visible light.</p>
<p class="p1" style="text-align: center;"><img src="images/Schermafbeelding_2016-08-08_om_08.37.15.png" alt="m15/4/CHEMI/HP3/eng/TZ2/28.a.ii"></p>
<div class="marks">[1]</div>
<div class="question_part_label">a.ii.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">Carotenoids may lose their colour and develop off odours when they are oxidized.</p>
<p class="p1">Identify, using table 22 of the data booklet, the structural feature that makes carotenoids susceptible to oxidation.</p>
<div class="marks">[1]</div>
<div class="question_part_label">b.i.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">List <strong>two </strong>factors which increase the rate of oxidation of carotenoids.</p>
<div class="marks">[2]</div>
<div class="question_part_label">b.ii.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">Deduce, giving a reason, whether carotenoids are water-soluble or fat-soluble.</p>
<div class="marks">[1]</div>
<div class="question_part_label">b.iii.</div>
</div>
<h2 style="margin-top: 1em">Markscheme</h2>
<div class="question" style="padding-left: 20px;">
<p class="p1">extensive conjugation/delocalization / extended system of conjugated double bonds/delocalized electrons;</p>
<p class="p1"><em>Accept “contains porphyrin/porphin ring”.</em></p>
<div class="question_part_label">a.ii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">multiple/conjugated <span style="text-decoration: underline;">C=C/carbon to carbon</span> double bonds;</p>
<div class="question_part_label">b.i.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">light;</p>
<p class="p1">higher/increased temperatures;</p>
<p class="p1">metals / transition metal ions;</p>
<p class="p1">hydroperoxides / peroxides;</p>
<p class="p1"><em>Accept acidity/low pH.</em></p>
<div class="question_part_label">b.ii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">fat-soluble <strong>and </strong>many non-polar groups/long non-polar chain;</p>
<p class="p1"><em>Accept fat-soluble </em><strong><em>and </em></strong><em>absence of hydroxyl/OH/polar/H-bonding groups.</em></p>
<div class="question_part_label">b.iii.</div>
</div>
<h2 style="margin-top: 1em">Examiners report</h2>
<div class="question" style="padding-left: 20px;">
<p class="p1">Though appreciation of the issue of complementary colours was widespread, hardly any candidates identified <strong>both </strong>absorption bands in the visible region. In the next few parts of the question many students lost marks by failing to answer fully, not referring to the <em>extensive </em>conjugation or the <em>large number </em>of <em>carbon-carbon </em>double bonds, as well as referring to temperature, rather than <em>increased </em>temperature, as a factor in the rate of oxidation. Lack of polarity was widely given as a reason for the fat solubility of carotenoids, though lack of groups able to form hydrogen bonds might have been more accurate (many quite polar molecules, such as \({\text{CHC}}{{\text{l}}_{\text{3}}}\), are insoluble in water). The features that lead to phospholipids acting as emulsifiers were often known, but again students tended to lose marks because their answers did not contain enough detail of their interaction between the phases present.</p>
<div class="question_part_label">a.ii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">Though appreciation of the issue of complementary colours was widespread, hardly any candidates identified <strong>both </strong>absorption bands in the visible region. In the next few parts of the question many students lost marks by failing to answer fully, not referring to the <em>extensive </em>conjugation or the <em>large number </em>of <em>carbon-carbon </em>double bonds, as well as referring to temperature, rather than <em>increased </em>temperature, as a factor in the rate of oxidation. Lack of polarity was widely given as a reason for the fat solubility of carotenoids, though lack of groups able to form hydrogen bonds might have been more accurate (many quite polar molecules, such as \({\text{CHC}}{{\text{l}}_{\text{3}}}\), are insoluble in water). The features that lead to phospholipids acting as emulsifiers were often known, but again students tended to lose marks because their answers did not contain enough detail of their interaction between the phases present.</p>
<div class="question_part_label">b.i.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">Though appreciation of the issue of complementary colours was widespread, hardly any candidates identified <strong>both </strong>absorption bands in the visible region. In the next few parts of the question many students lost marks by failing to answer fully, not referring to the <em>extensive </em>conjugation or the <em>large number </em>of <em>carbon-carbon </em>double bonds, as well as referring to temperature, rather than <em>increased </em>temperature, as a factor in the rate of oxidation. Lack of polarity was widely given as a reason for the fat solubility of carotenoids, though lack of groups able to form hydrogen bonds might have been more accurate (many quite polar molecules, such as \({\text{CHC}}{{\text{l}}_{\text{3}}}\), are insoluble in water). The features that lead to phospholipids acting as emulsifiers were often known, but again students tended to lose marks because their answers did not contain enough detail of their interaction between the phases present.</p>
<div class="question_part_label">b.ii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">Though appreciation of the issue of complementary colours was widespread, hardly any candidates identified <strong>both </strong>absorption bands in the visible region. In the next few parts of the question many students lost marks by failing to answer fully, not referring to the <em>extensive </em>conjugation or the <em>large number </em>of <em>carbon-carbon </em>double bonds, as well as referring to temperature, rather than <em>increased </em>temperature, as a factor in the rate of oxidation. Lack of polarity was widely given as a reason for the fat solubility of carotenoids, though lack of groups able to form hydrogen bonds might have been more accurate (many quite polar molecules, such as \({\text{CHC}}{{\text{l}}_{\text{3}}}\), are insoluble in water). The features that lead to phospholipids acting as emulsifiers were often known, but again students tended to lose marks because their answers did not contain enough detail of their interaction between the phases present.</p>
<div class="question_part_label">b.iii.</div>
</div>
<br><hr><br><div class="specification">
<p>Nuclear reactions transform one nuclide into another. Fission, splitting a large nucleus into two smaller nuclei, releases vast amounts of energy.</p>
</div>
<div class="question">
<p>(i) Uranium hexafluoride, UF<sub>6</sub>, is used in the uranium enrichment process that produces fuel for nuclear reactors.</p>
<p>State the molecular shape of uranium hexafluoride.</p>
<p>(ii) Explain why uranium dioxide, UO<sub>2</sub>, has a very high melting point whereas uranium hexafluoride vapourises easily into gas.</p>
</div>
<h2 style="margin-top: 1em">Markscheme</h2>
<div class="question">
<p>i</p>
<p>octahedral</p>
<p><em>Accept “square bipyramidal”</em></p>
<p> </p>
<p>ii</p>
<p>UO<sub>2</sub> strong bonding throughout crystal structure</p>
<p>UF<sub>6</sub> molecular «covalent bonds between atoms» <em><strong>AND</strong></em> London/dispersion/instantaneous induced dipole-induced dipole forces between molecules </p>
<p><em>Accept “UO<sub>2</sub> has ionic lattice”</em></p>
<p> </p>
</div>
<h2 style="margin-top: 1em">Examiners report</h2>
<div class="question">
[N/A]
</div>
<br><hr><br><div class="specification">
<p class="p1">The oxygen levels in water can change for a number of reasons.</p>
</div>
<div class="specification">
<p class="p1">The use of phosphate fertilizers can also produce changes in the oxygen concentrations in a river.</p>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">Phosphate ions can be removed from a solution by adding calcium ions. State the ionic equation for the reaction of calcium ions with phosphate ions.</p>
<div class="marks">[1]</div>
<div class="question_part_label">b.i.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1">Deduce the expression for the solubility product constant, \({K_{{\text{sp}}}}\), of calcium phosphate.</p>
<div class="marks">[1]</div>
<div class="question_part_label">b.ii.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p class="p1"><span class="s1">The solubility product of calcium phosphate is \({\text{2.07}} \times {\text{1}}{{\text{0}}^{ - 33}}\) </span>at 298 K. Determine the concentration, in \({\text{mol}}\,{\text{d}}{{\text{m}}^{ - 3}}\), of calcium ions, \({\text{C}}{{\text{a}}^{2 + }}\), in a saturated aqueous solution of calcium phosphate.</p>
<div class="marks">[3]</div>
<div class="question_part_label">b.iii.</div>
</div>
<h2 style="margin-top: 1em">Markscheme</h2>
<div class="question" style="padding-left: 20px;">
<p class="p1">\({\text{3C}}{{\text{a}}^{{\text{2 + }}}}{\text{(aq)}} + {\text{2PO}}_{\text{4}}^{3 - }{\text{(aq)}} \rightleftharpoons {\text{C}}{{\text{a}}_{\text{3}}}{{\text{(P}}{{\text{O}}_{\text{4}}}{\text{)}}_{\text{2}}}{\text{(s)}}\);</p>
<p class="p1"><em>Ignore state symbols</em>.</p>
<p class="p1"><em>Accept single arrow sign</em>.</p>
<div class="question_part_label">b.i.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">\({\text{(}}{K_{{\text{sp}}}} = {\text{) [C}}{{\text{a}}^{2 + }}{{\text{]}}^3}{{\text{[PO}}_4^{3 - }{\text{]}}^2}\);</p>
<p class="p1"><em>Ignore state symbols</em>.</p>
<p class="p1"><em>Do not award mark if incorrect brackets are used or are missing.</em></p>
<div class="question_part_label">b.ii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">Let <span class="s1"><em>x </em></span>be solubility so \(2.07 \times {10^{ - 33}} = {(3x)^3}{(2x)^2}\);</p>
<p class="p1"><em>Remember to apply ECF from (ii).</em></p>
<p class="p1">\({x^5} = \frac{{2.07 \times {{10}^{ - 33}}}}{{(27 \times 4)}}/1.92 \times {10^{ - 35}}/x = 1.14 \times {10^{ - 7}}\);</p>
<p class="p1">\(\left( {[{\text{C}}{{\text{a}}^{2 + }}] = 3x = } \right){\text{ }}3.42 \times {10^{ - 7}}{\text{ (mol}}\,{\text{d}}{{\text{m}}^{ - 3}}{\text{)}}\);</p>
<p class="p1"><em>Award </em><strong><em>[3] </em></strong><em>for final correct answer</em>.</p>
<div class="question_part_label">b.iii.</div>
</div>
<h2 style="margin-top: 1em">Examiners report</h2>
<div class="question" style="padding-left: 20px;">
<p class="p1">Q was only identified by the stronger candidates and even then few stated that waste needs oxygen to decompose. The ionic equation for the reaction of calcium ions with phosphate ions proved a real minefield. It was highly disappointing at HL that so many candidates did not know what the formula and charge of the phosphate anion actually is. Some gave phosphite and several gave phosphide. Core chemistry underpins all options and candidates need to be prepared to apply some basic chemical principles to the various topics in the options. This aspect will be further enhanced in the new chemistry syllabus, but performance of candidates in this particular question shows the importance of this even in the current syllabus. In (ii), candidates often used the ionic equation in (i) to write the solubility product expression and hence had an incorrect inverse equation. Many also did not realize that the activity of a species in the solid state is unity. In (iii), incorrect \({K_{{\text{sp}}}}\) expressions in (ii) threw some candidates and others could not deal with the math involved in the solution to the equation. Many thought the final answer was x and not 3x for \({\text{[C}}{{\text{a}}^{2 + }}{\text{]}}\). Of course the stronger candidates scored all three marks on this question. In (c), misreading of the question was common which specifically asked for a non-chemical reason for the decrease in oxygen concentration <em>i.e. </em>an increase in the temperature of the water.</p>
<div class="question_part_label">b.i.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">Q was only identified by the stronger candidates and even then few stated that waste needs oxygen to decompose. The ionic equation for the reaction of calcium ions with phosphate ions proved a real minefield. It was highly disappointing at HL that so many candidates did not know what the formula and charge of the phosphate anion actually is. Some gave phosphite and several gave phosphide. Core chemistry underpins all options and candidates need to be prepared to apply some basic chemical principles to the various topics in the options. This aspect will be further enhanced in the new chemistry syllabus, but performance of candidates in this particular question shows the importance of this even in the current syllabus. In (ii), candidates often used the ionic equation in (i) to write the solubility product expression and hence had an incorrect inverse equation. Many also did not realize that the activity of a species in the solid state is unity. In (iii), incorrect \({K_{{\text{sp}}}}\) expressions in (ii) threw some candidates and others could not deal with the math involved in the solution to the equation. Many thought the final answer was x and not 3x for \({\text{[C}}{{\text{a}}^{2 + }}{\text{]}}\). Of course the stronger candidates scored all three marks on this question. In (c), misreading of the question was common which specifically asked for a non-chemical reason for the decrease in oxygen concentration <em>i.e. </em>an increase in the temperature of the water.</p>
<div class="question_part_label">b.ii.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p class="p1">Q was only identified by the stronger candidates and even then few stated that waste needs oxygen to decompose. The ionic equation for the reaction of calcium ions with phosphate ions proved a real minefield. It was highly disappointing at HL that so many candidates did not know what the formula and charge of the phosphate anion actually is. Some gave phosphite and several gave phosphide. Core chemistry underpins all options and candidates need to be prepared to apply some basic chemical principles to the various topics in the options. This aspect will be further enhanced in the new chemistry syllabus, but performance of candidates in this particular question shows the importance of this even in the current syllabus. In (ii), candidates often used the ionic equation in (i) to write the solubility product expression and hence had an incorrect inverse equation. Many also did not realize that the activity of a species in the solid state is unity. In (iii), incorrect \({K_{{\text{sp}}}}\) expressions in (ii) threw some candidates and others could not deal with the math involved in the solution to the equation. Many thought the final answer was x and not 3x for \({\text{[C}}{{\text{a}}^{2 + }}{\text{]}}\). Of course the stronger candidates scored all three marks on this question. In (c), misreading of the question was common which specifically asked for a non-chemical reason for the decrease in oxygen concentration <em>i.e. </em>an increase in the temperature of the water.</p>
<div class="question_part_label">b.iii.</div>
</div>
<br><hr><br><div class="specification">
<p>Low density polyethene (LDPE) and high density polyethene (HDPE) are both addition polymers.</p>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>Describe how the monomers of addition polymers and of condensation polymers differ.</p>
<div class="marks">[1]</div>
<div class="question_part_label">b.</div>
</div>
<div class="question" style="padding-left: 20px; padding-right: 20px;">
<p>Identify the type of intermolecular bonding that is responsible for Kevlar<sup>®</sup>’s strength.</p>
<div class="marks">[1]</div>
<div class="question_part_label">c.</div>
</div>
<h2 style="margin-top: 1em">Markscheme</h2>
<div class="question" style="padding-left: 20px;">
<p><em>addition:</em> C=C</p>
<p><em><strong>AND</strong></em></p>
<p><em>condensation:</em> two functional groups needed on each monomer</p>
<p>Accept "alkene/alkenyl" <em><strong>OR</strong> </em>"double bond" <em><strong>OR</strong> </em>"multiple bond".</p>
<div class="question_part_label">b.</div>
</div>
<div class="question" style="padding-left: 20px;">
<p>hydrogen bonds</p>
<p><em>Accept “\(\pi - \pi \) stacking/interactions”.</em></p>
<div class="question_part_label">c.</div>
</div>
<h2 style="margin-top: 1em">Examiners report</h2>
<div class="question" style="padding-left: 20px;">
[N/A]
<div class="question_part_label">b.</div>
</div>
<div class="question" style="padding-left: 20px;">
[N/A]
<div class="question_part_label">c.</div>
</div>
<br><hr><br>